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3 Answers
3

The usual convention is that numbers up to twenty are written out - as I just did with the word "twenty". The same is true for numbers that are said as a single phrase like "fifteen" or "five hundred" or "forty thousand".

Other than that, use figures. 1970's, not "Nineteen-seventies". 3.30pm, not "three-thirty p.m.". However "I'll see you at three", not "I'll see you at 3". Decade names such as "the sixties" or "the 50's" could go either way.

The rule of thumb would be, does it feel natural to say the number in a single breath? If so, write it out. Having the numbers written out means that the continuous flow of text is not disrupted. If, however, the numbers are longer so that you would need a great long string of text to write them out, it's much more convenient to use numerals.

There are exceptions and borderline cases. Sometimes text that would usually be in numerals can be written out for emphasis. "That number wasn't 549, you twit. It was 594. Five-nine-four."

The "twenty" line in the sand seems a bit arbitrary. For instance, it indicates you should use "three-fifteen" but fifteen minutes later should be written "3:30". I don't have good style-guide backing for this but it seems logical to me to use words for any "everyday" number, which I'd define as any number up to a hundred and any power of ten after that. That would mean you write out most numbers in a narrative except for decimals (like money), years (though I'd just use "the seventies" in your example unless the story is far-future) or strings of digits (phone numbers etc).
– KeithSNov 13 '15 at 17:19

@KeithS, I concede it is a bit arbitrary - but it's one of those situations in which the exact value of a cut-off point is of much less practical importance than that there is a cut-off point. (If I am correct in thinking that you work in the legal field you must surely be familiar with similar situations in laws defining adulthood, statutes of limitations and so on.) Having a "rule" allows the writer to avoid spending too much time worrying about the inevitable doubtful cases and get on with real writing. But it's only a rule of thumb, not a rule of law. If breaking it feels right, do so.
– LostinfranceNov 16 '15 at 20:15

I would recommend using a style guide and being consistent. I use THE CHICAGO MANUAL OF STYLE which Is very different from AP on this subject. Also, I would have differences in narrative versus dialogue:

There was a 150-ton truck blocking the path

but, "Did you know that there is a hundred-and-fifty-ton truck in our path?"

Certain things should be ordinals in either case (brands and whatnot):

My copy of MLA Handbook says to write out numbers that can be expressed in one or two words, and use numerals for those that require more. So "fifteen" and "twenty-one" but "102" and "3 1/2".

They further state to always use numerals with a symbol or abbreviation, so "$10" and "4 p.m." and "8 kg". Also use numerals in addresses -- "14 Elm Street" -- and dates.

I've also heard the "up to twenty" rule frequently cited. It would give similar results, though exceptions would be "twenty-one" and "two thousand". Personally I'll normally write "a thousand" or "one thousand" rather than "1,000" in most cases.

Another common rule is that if you give several numbers, and some of them are big enough to call for numerals, then you should use numerals for all. That is, it is inconsistent to write something like, "The results of our counts were sixteen, 124, and one hundred." Once you resort to numerals, make everything related numerals.

Thanks very much Jay, Stu and Lost in France - very useful. The only one I'm hesitating about is the height one. Would you recommend writing: They are both 6'2" or they are both six foot two?
– MoniqueHNov 14 '15 at 6:07

Am I right in thinking it's better to write: "It's early 1900's" rather than "It's early nineteen hundreds"?
– MoniqueHNov 14 '15 at 6:29

Does it make a difference if the character is saying the number rather than the number being part of the description. E.g. Would it work to say, "I want to get $400 for this one." or should the character say, "I want to get four hundred for this one"? Sorry, am second-guessing myself a lot!
– MoniqueHNov 14 '15 at 6:30

1

All your examples are matters of taste and others might disagree, but personally in a novel I'd write "six foot two" and "early nineteen hundreds"; in a factual report, or other non-fiction document such as stage directions, I would write 6'2" and "early 1900's". I'd definitely write out "I want to get four hundred", particularly if, as in your example, the character casually omits the word "dollars" - that omission provides some information about his or her personality, style of speech and mood at that moment.
– LostinfranceNov 14 '15 at 8:10

I agree. I write out all my numbers in dialogue with a couple of exceptions: particular years ("I graduated in 1952"), proper names or documents ("After Title IX, there was no way I could get a scholarship in track"), or when it follows by convention ("My favorite Grateful Dead show was 6/9/77 [this is how a fan would write it]"). If it's fiction, you make the rules until the publisher replaces them.
– Stu WNov 15 '15 at 2:28